The invention relates to a method of manufacturing a semiconductor device whereby a first layer of silicon oxide is deposited on a surface of a silicon body and is provided with contact windows within which semiconductor zones formed in the semiconductor body and conductor tracks of non-crystalline silicon formed on the surface are exposed, while on said first layer of silicon oxide a first metallization layer is formed which makes contact in the contact windows with the active semiconductor zones and with the conductor tracks of non-crystalline silicon and which is covered with a second layer of silicon oxide which is provided with contact windows within which the first metallization layer is exposed, whereupon consecutively an adhesion layer is deposited on the second layer of silicon oxide and in the contact windows formed therein, the contact windows are filled with tungsten plugs, and a second metallization layer is formed on the layer of insulating material so as to make contact with the tungsten plugs formed in the contact windows.
The conductor tracks of non-crystalline silicon may be formed in a layer of polycrystalline silicon, but also in a layer of amorphous silicon. The tungsten plugs may be formed in the contact windows in the second layer of silicon oxide in that a thick layer of tungsten is deposited, which is subsequently subjected to an etching treatment until the adhesion layer next to the contact windows has become exposed again. Instead of the etching treatment, a chemical-mechanical polishing treatment may be used.
Such a method is known from U.S. Pat. No. 5,529,955, wherein the first metallization is formed by an Al layer or a layer of an alloy of Al with Si and Cu, while the adhesion layer used is a layer comprising one or several materials from the group of Ti, TiN, TiW, and WSi. Preferably, a laminate of layers from said group of materials is used as the adhesion layer, such as a layer of Ti on which a layer of TiN is deposited.
It is a disadvantage of the use of Al or said alloy of Al as a first metallization layer that the contact between the semiconductor zones and the metallization can change during operation of the semiconductor device owing to electromigration.
The invention has for its object inter alia to counteract the above disadvantage. The method mentioned in the opening paragraph is for this purpose characterized in that the first metallization layer is formed in a tungsten layer, while a layer of titanium nitride is deposited as the adhesion layer on the second layer of silicon oxide and in the contact windows formed therein.
The first metallization layer is formed in a layer of tungsten. No change occurs in the contact resistance between the semiconductor zones and the conductor tracks connected thereto during operation of the semiconductor device if a layer of tungsten is used. In addition, the layer of silicon oxide to be formed on the first metallization layer can be deposited at a comparatively high temperature on a layer of such a refractory metal without causing damage to the metallization. A thin and dense layer of silicon oxide may thus be formed. A problem arises, however, if the preferably used adhesion layer consisting of a laminate of a layer of Ti on which a layer of TiN is deposited is used in the formation of tungsten plugs on a first metallization layer of tungsten in the known method as described above. It is found that a contact resistance measured between the first metallization of tungsten and the tungsten plugs formed in the contact windows in the layer of silicon oxide deposited thereon on the first metallization layer has a considerable spread over the plugs. This spread may be so great that the method is unsuitable for use in the manufacture of semiconductor devices. It was surprisingly found that the use of an adhesion layer exclusively consisting of TiN leads to said spread being much smaller, which results in the method being suitable for use in the manufacture of semiconductor devices.
Preferably, the first metallization layer is formed in a tungsten layer which is deposited on an adhesion layer which is formed on the first layer of silicon oxide and in the contact windows formed therein and which consists of a layer of titanium and a layer of titanium nitride deposited thereon. If the adhesion layer consisting of a laminate of a layer of Ti on which a layer of TiN is deposited is used, the contact resistance between the semiconductor zones and the first metallization layer, as seen over the contact windows in the first layer of silicon oxide, will have only a small spread. The use of an adhesion layer purely made of TiN is found to make the spread in the contact resistance greater here.
A low contact resistance between the semiconductor zones and the first metallization is obtained if the active semiconductor zones and the conductor tracks of non-crystalline silicon which are formed on the surface and with which the first metallization makes contact are provided with a top layer of titanium disilicide before the deposition of the first layer of silicon oxide.